- 2909 - STARS - extreme stars, examples? Stars in the night sky look pretty stable. Not much going on out there. But, it is worthy of a closer look to really learn what is beyond our nightly vision. Here are some examples of extreme stars. Be thankful our Sun is not one of them
--------------------------- 2909 - STARS - extreme stars, examples
- Our Sun is a pretty boring star. Still burning through the hydrogen in its core, our middle-aged Sun is comfortable at its current, relatively petite size. And though it will stay this way for about 5 billion years more, our star will eventually run low on hydrogen and switch to fusing helium deep within.
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- When hydrogen and helium are all used up by fusion into heavier elements this happens. Fusion will inflate our Sun into a “red giant star” over the span of just a couple of hundred million years. After engulfing the innermost planets, possibly including Earth, the Sun will continually shed its outer layers, eventually leaving behind a smoldering “white dwarf star” surrounded by a beautiful “planetary nebula” of glowing gas.
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- That’s the picturesque life that most stars live. Now let’s take quick review of some of the universe’s most extreme stars:
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- The biggest is UY Scuti. The supergiant stars. a fitting category for the largest known star in the universe. One day, the Sun will become a “red giant“. But if it had started its life with a dozen or so times its current mass, it could have eventually evolved into a red supergiant.
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- UY Scuti has already shed a lot of mass. Hypergiants stars can swell to more than 1,000 times the size of the Sun. UY Scuti, located near the center of the Milky Way in the constellation Scutum, is around 1,700 times the Sun’s width.
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- In 1860 astronomers catalogued this star. But later, researchers noticed UY Scuti’s brightness changes over a period of about 740 days, leading them to classify it as a “variable star“.
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- Some of these variable stars vary in brightness for external reasons, such as being eclipsed by another star or clouds of gas and dust from our vantage point. However, intrinsic variables like UY Scuti experience physical changes within, such as pulsations. UY Scuti varies in brightness because it’s constantly yo-yoing in terms of size.
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- But like any red super giant, including Betelgeuse our closest red giant, UY Scuti is destined to end its life with a bang. After exhausting the helium fuel in its core, it will forge increasingly heavy elements. And as long as UY Scuti doesn’t expel too much mass over the course of its remaining life, it will eventually start producing iron.
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- Making iron is a death sentence for stars. Unlike when it combines lighter elements, when a star forces two iron nuclei together, it doesn’t release any energy; it instead takes energy away from the environment. This causes a runaway collapse where the star no longer generates enough outward pressure to keep it from imploding under its own gravity.
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- The end result? A powerful core-collapse (type II) supernova that will finally make UY Scuti visible to the naked eye from Earth.
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- Massive and luminous stars like RMC 136a1 sport extremely powerful stellar winds, which are streams of charged particles flowing from the star’s surface. They also emit intense ultraviolet radiation that would be strong enough to sterilize the surface of Earth.
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- Looks can be deceiving. Just because a star is a certain size doesn’t mean it has a certain mass. That’s absolutely the case with the most massive known star in the universe , RMC 136a1, which packs a lot of power into a surprisingly small volume. Although thought to be more than 300 times the mass of our Sun, RMC 136a1 is only about 30 times as wide as our home star.
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- Located in the Milky Way’s largest satellite galaxy, the Large Magellanic Cloud, RMC 136a1 is just one of many blazing stars that’s ionizing the gas within NGC 2070. This huge open star cluster lies in the heart of the Tarantula Nebula, which is the brightest star-forming region in our galactic neighborhood.
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- Hubble Space Telescope observations have shown that RMC 136a1 is just one of more than 200 bright, massive stars in the immediate area, all found within a cluster called RMC 136. However, RMC 136a1 is the brightest of these beacons. In addition to holding the title for the most massive star, RMC 136a1 also takes the crown for the most luminous star.
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- Although the exact age is still uncertain, according to a 2016 study, RMC 136a1 could be as young as a few hundred thousand to a million years old, so it’s thought to still be burning hydrogen in its core. And because RMC 136a1 is a rare “Wolf-Rayet star“, it’s incredibly hot, full of heavy elements, and has extremely powerful stellar winds that are blowing off its outer layers.
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- These stellar winds are so powerful, reaching a velocity of around 5.8 million miles per hour, and by the end of its life, the star is expected to expel enough gas to end up weighing just over 50 solar masses. However, that’s still plenty big enough to produce an astounding supernova. The progenitor of Supernova 1987A, also located in the Large Magellanic Cloud, was only about 20 solar masses.
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- Astronomers found tiny star EBLM J0555-57Ab only when it passed in front of its larger binary companion, which blocked some of the bigger star’s light. Detecting such a transit is also the way researchers find many exoplanets.
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- If a star is exceptionally massive, it gobbles up its fuel, causing it to live fast and die hard. However, if a star is small and light, it has a slow metabolism, allowing it to live an extremely long life. But just how small can a star be? EBLM J0555-57Ab is right at the limit.
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- At just 85 times the mass of Jupiter and a sliver wider than Saturn, EBLM J0555-57Ab skirts the lower boundary of what it takes to be a star. Had the star formed with only a slightly lower mass, the fusion reaction of hydrogen in its core could not be sustained, and the star would instead have transformed into a brown dwarf star.
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- Although not well understood, brown dwarfs are not-quite-planets, not-quite-stars whose cores can only fuse a heavy form of hydrogen called deuterium, as well as possibly lithium.
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- EBLM J0555-57Ab may be tiny, but there are other stars out there that compare with its puny mass. For example:, the star TRAPPIST-1, which hosts at least seven rocky planets, tips the scales at 0.089 M, just a little more massive than EBLM J0555-57Ab.
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- Because stars with less than 25 percent the Sun’s mass are the most common type of stars and excellent candidates for hosting Earth-sized planets, learning more about the lives of the smallest stars may help researchers uncover potentially habitable, Earth-like planets around them.
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- The hottest is WR 102. The faster a star burns through its fuel, the shorter its life. And this is surely the case for Wolf-Rayet stars. These stars not only burn incredibly hot and bright, but their stellar winds also blast much of their potential fuel into space. The hottest known star, WR 102, is one such Wolf-Rayet, sporting a surface temperature more than 35 times hotter than the Sun.
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- Wolf-Rayet stars come in a variety of flavors. The most massive star, RMC 136a1, has a spectral type of WN, meaning it’s rich in ionized nitrogen as a result of rapidly converting hydrogen to helium in its fiery core via the C-N-O cycle.
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- The hottest star, WR 102, is an especially rare WO-type Wolf-Rayet, which is a late-stage star that has a surface heavily enriched with ionized oxygen. Astronomers only know of about 10 WO-type Wolf-Rayet stars in the entire universe.
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- Even for a Wolf-Rayet star, WR 102 has intense stellar winds. Currently, they are blowing about a Sun’s worth of mass from the star’s surface every 100,000 years. That means WR 102 is losing several hundred million times more mass each year than the Sun. WR 102 would be completely gone in less than 2 million years.
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- Astronomers are interested in WR 102 not just because of its exceptionally hellish surface temperature and rapid mass loss, but also because the star is a prime candidate to go supernova in the relatively near future. WR 102 is a post-core helium burning star and has a remaining lifetime of less than 2,000 years.”
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- The fastest is S5-HVS1. The Sun zips through space at a brisk 490,000 mph relative to the Milky Way. The fastest known star (that’s not a white dwarf) belongs to a speed demon known as S5-HVS1. This middle-aged, hypervelocity star is fleeing our galaxy at more than 3.9 million mph. That is about 0.6 percent the speed of light.
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- Astronomers first found the star streaking through the southern constellation Grus in 2019. After tracing its orbit back in time, they quickly realized it is coming from the center of the Milky Way, near our roughly 4-million-solar-mass supermassive black hole, Sagittarius A*.
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- Astronomers think the black hole ejected the star with a speed of thousands of kilometers per second about 5 million years ago. This ejection happened at the time when humanity’s ancestors were just learning to walk on two feet.
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- Researchers suspect S5-HVS1 wasn’t always alone. The evidence suggests the star was ejected thanks to a process called the ‘Hills mechanism“, which was outlined some three decades ago by astronomer Jack Hills.
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- The Hills mechanism idea is that S5-HVS1 was once part of a binary system that orbited Sagittarius A*. When the stellar pair ventured too close, the black hole captured the companion star, releasing S5-HSV1 from its binary dance and flinging it through space.
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- November 22, 2020 2909
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